An optical transmission system, in part, comprises a series of optical fiber cables. The transmission system uses an optical coupling disclosed in European Published Specification No. 0128044, published on Dec. 12, 1984 to couple together the ends of each corresponding pair of cables in the series. A need exists for a transmitter, to generate an optical test signal, and for a receiver, potentially remote from the transmitter to test for continuity of the test signal propagating along the cables. A further need exists for the receiver to assist in tuning, which is defined as adjusting one cable with respect to the other cable in the coupling to make an adjustment in alignment of the ends of the corresponding pair of cables. Tuning assures that the ends of the cables are aligned to reduce losses in optical signals that are transferred from one cable to another.